I really have no idea what is happening with your son, but I had some serious back issues a few years ago that damaged my sciatic nerve. I can tell you that the pain can "jump" along the sciatic nerve. The sciatic nerve ends in the foot. Sometimes, I would get a shooting pain up through the bottom of my foot in the middle, like I had just stepped on a nail. Also, nerve damage can cause numbness. I still have numbness on the outside of my left calf because of the ordeal.
So, since you know he has scoliosis, maybe you should check to see if is affecting any nerves. There are tests that can identify the specific nerves affected.